In order to protect their surface from damage caused by abrasion, optical fibers are typically coated with one or more polymers as they are drawn. Typically the fibers are drawn from a heated glass blank and coated by an in-line process before they come into contact with any solid surface. Prior to coating, however, the fiber must be allowed to cool. If the fiber's temperature is too high it cannot be coated in a stable fashion by conventional materials used for coating such fibers. Therefore in current practice tall draw towers, 25 meters or more in height, are employed in order to provide sufficient distance for convection cooling of the fiber. The speed at which this drawing and coating process can be run is limited by the need to cool the fiber to a temperature that does not cause detriment to the coating polymer(s) (See, for example, Polymers for High Technology, ACS Symposium Series: 346, Chapter 34, p. 410, American Chemical Society, Washington, DC (1987) and Levin et al., The Effects of Cure Temperature on The Reaction Kinetics and Elastic Modulus of a UV-Cured Acrylate System, Polym. Mater. Sci. Eng. (1995) 72:524-525). The present inventors have unexpectedly found that radiation curable compositions comprising an alkenyl ether functional polyisobutylene can be cured at higher temperatures than those compositions used in traditional commercial processes to coat such fibers, and therefore can result in faster throughput for processing equipment. In addition, it has been found that such coatings can readily be overcoated with acrylate functional polymers.
Polyisobutylenes containing functional groups which are radiation curable have been disclosed in the art. For example, T. P. Liao and J. P. Kennedy in Polymer Bulletin, V. 6, pp. 135-141 (1981) disclose acryl and methacryl telechelic polyisobutylenes having the formula CH.sub.2.dbd.C(R)--COO--PIB--OOC--C(R).dbd.CH.sub.2 where R is --H or CH.sub.3. These materials were prepared by reacting alpha, omega di-hydroxypolyisobutylene, HOCH.sub.2 --PIB--CH.sub.2 OH, and excess acryloyl or methacryloyl chloride. These prepolymers are disclosed as being useful in the synthesis of a variety of new composites containing a soft polyisobutylene segment.
J. P. Kennedy and B. Ivan in Polymer Material Science and Engineering, V. 58, p.866 (1988) disclose allyl telechelic linear and star-branched polyisobutylenes prepared by a convenient rapid one pot polymerization functionalization process. The polymerization step involved living polymerization of isobutylene by recently discovered mono- or multifunctional initiating systems (combinations of tert-ester and ether/Lewis acids) followed by electrophilic functionalizations by allyltrimethylsilane in the presence of TiCl.sub.4. Characterization indicated quantitative end allylations. Subsequent quantitative derivations of the allyl termini yielded mono-, di-, and tri-functional hydroxyl- and epoxy-telechelic polyisobutylenes which could be cured to rubbery networks.
J. P. Kennedy and B. Ivan in the Journal of polymer Science, Part A, Polymer Chemistry, V. 28, p. 89 (1990) disclose mono-, di-ended linear, and three-arm star allyl telechelic polyisobutylenes which are prepared by a rapid economical one-pot polymerization-functionalization process. The process involved the living polymerization of isobutylene by mono-, di-, or tri-functional initiating systems, specifically by aliphatic and aromatic tert-ester and -ether/TiCl.sub.4 combinations, followed by electrophilic functionalization of the living sites with allyltrimethylsilane. Quantitative derivations of the ally termini yielded mono-, di-, and tri-epoxy and -hydroxy-telechelic polyisobutylenes. It is further disclosed that strong rubbery networks were made by curing the epoxy-telechelic polyisobutylenes with triethylene tetramine and by reacting the hydroxy-telechelic polyisobutylenes with MDI.
J. P. Kennedy et al., in Polymer bulletin, V. 25, p. 633 (1991) disclose vinyl ether terminated polyisobutylene macromonomers. However, no mention was made regarding radiation curable compositions based on these macromonomers. It is known that radiation cured networks from non-telechelic chain end functional macromonomers possess poor physical properties.
N. A. Merrill, I. J. Gardner, and V. L. Hughes in RadTech North America Proceedings, V. 1, pp. 77-85 (1992) disclose conjugated diene functional polyisobutylenes which have a high reactivity to both ultraviolet and electron beam radiation. These conjugated diene functional polyisobutylenes, alone or in a formulation, are disclosed as being useful in preparing pressure sensitive adhesives.
In PCT Patent Publication No. WO 9104992 is disclosed a functionalized copolymer of isobutylene and a para-methylstyrene, wherein at least one type of functional group is attached to the para-methyl group of the para-methylstyrene, the copolymer having a substantially homogenous compositional distribution. The functionalized groups are exemplified by alkoxides, phenoxides, carboxylates, thiolates, thiopenolates, thioethers, thiocarboxylates, dithiocarboxylates, thioureas, dithiocarbamates, xanthanates, thiocyanates, silanes, halosilanes, malonates, cyanides, amides, amines, carbazoles, phthalimides, pyridine, maleimide, cyanates, and phosphines.
In PCT Patent Publication No. WO 9211295 is disclosed a radiation reactive functionalized polymer comprising an isoolefin having about 4 to about 7 carbon atoms and a para-alkylstyrene, wherein a radiation reactive functional group is attached to the para-alkyl group of the para-alkylstyrene, and discloses radiation curable pressure sensitive adhesives comprising the functionalized polymer and a tackifier. In WO'295, the radiation curable groups are disclosed as being groups such as thioxanthones, acrylates, aldehydes, ketones, and esters.
Saxena et al., U.S. Pat. No. 5,665,823, disclose a method for preparing an acrylic functional polyisobutylene polymer or copolymer, the method comprising reacting a polyisobutylene polymer or copolymer which contains at least one carbon-bonded silanol group in it molecule with a silane having both an acrylic-containing group and a silicon-bonded hydrolyzable group in its molecule.
Furthermore, radiation curable compositions which contain vinyl ether functional organosilicon compounds have also been described in the art. For example, Crivello in U.S. Pat. No. 4,617,238 discloses a photopolymerizable composition comprising (a) an organopolysiloxane having at least one Si-bonded vinyloxy functional group of the formula H.sub.2 C.dbd.CH--O--G--, where G is alkylene (such as propylene) or alkylene interrupted by at least one divalent heteroradical selected from --O--, divalent phenylene, or substituted divalent phenylene, or combination of such heteroradicals, and (b) an onium salt catalyst. The '238 patent also describes a method wherein the vinyl ether group is introduced into the organopolysiloxane by addition (hydrosilylation) of compounds with an allyl and a vinyl ether group to an SiH group of the organopolysiloxane in the presence of a platinum catalyst. In the method of the '238 patent, only the allyl group is added to the SiH group while the vinyl ether group is preserved and thus only one vinyl ether group for each SiH group can be incorporated into the siloxane molecule at any given time.
European Patent Publication No. 0462389 teaches thermosetting organopolysiloxanes with oxyalkylene vinyl ether groups bonded by SiOC groups and the vinyl groups may be substituted by alkyl groups. EPO'389 also teaches a method for the preparation of these compounds and their application as photochemically thermosetting polysiloxanes in encapsulating compounds, as non-stick coating compounds for flat carriers or as modified additives in compounds which can be thermoset radically, cationically, or by UV or electron radiation.
Brown et al., U.S. Pat. No. 5,270,423, disclose organosilicon compounds with a siloxane portion of the general formula --OR'OCH.dbd.CHR" linked via an SiOC bond wherein R' is a divalent hydrocarbon group and R" is hydrogen or an alkyl group which are useful in radiation curable compositions, in which they are mixed with an initiator. The compositions are particularly useful in UV radiation curable coatings.
Glover et al., U.S. Pat. No. 5,594,042, disclose radiation curable compositions comprising vinyl ether functional siloxanes and aromatic iodonium salt or aromatic sulfonium salt photoinitiators which cure upon exposure to ultraviolet or electron beam radiation. The vinyl ether groups are linked to the silicon atom on the siloxane through an SiOC bond and the photoinitiators are disclosed as being preferably either diaryliodonium salts of sulfonic acids or triarylsulfonium salts of sulfonic acids.
Bujanowski et al., U.S. Pat. No. 5,629,095, disclose vinyl ether functional siloxane resins, radiation curable coating compositions comprising a vinyl ether functional siloxane resin and a photocleavable acid, and a coated article obtained by applying the radiation curable coating composition to a substrate and then exposing the coating to radiation in an amount sufficient to cure the coating. In the '095 patent, the vinyl ether group in the siloxane resin is attached to the silicone atom through an SiOC bond.
Bishop et al., U.S. Pat. No. 4,514,037, disclose coating compositions for optical glass fiber which comprise 30% to about 80% of linear diacrylate-functional polyurethanes which are the reaction product of polycarbonate diol with organodiisocyanate. The linear polyurethanes are end-capped with acrylate groups and are used in combination with at least 15% monoethylenically unsaturated monomer having a glass transition temperature above about 55.degree. C.
Shustack, U.S. Pat. No. 5,536,529, describes ultraviolet radiation-curable coatings for optical fibers and optical fibers coated therewith. The primary coating comprises a hydrocarbon polyol-based reactively terminated aliphatic urethane oligomer; a hydrocarbon monomer terminated with at least one end group capable of reacting with the terminus of the oligomer; and an optional photoinititator. The secondary coating comprises a polyester and/or polyether-based aliphatic urethane reactively terminated oligomer (I); a hydrocarbonaceous viscosity-adjusting component capable of reacting with the reactive terminal of (I); and an optional photoinitiator.
Bahadur et al. U.S. patent application Ser. No. 09/200,038, describe a method for making alkenyl ether functional polyisobutylene polymers which are useful in curable compositions for forming coatings, sealants, caulks, adhesives, and paints.
Bahadur et al., U.S. patent application Ser. No. 09/199,261, describe radiation curable compositions suitable for coating optical fibers comprising an alkenyl ether functional polyisobutylene, a cationic photoinitiator, a free radical photoinitiator, and optionally an alkenyl ether compound which is free of isobutylene units.